The pandemic has gone through several twists and turns, and is far from over. With emphasis on reinfections, this article examines some of the latest research findings, and how that could shape our future.
1. The changing narrative about COVID vaccines
In the beginning of the pandemic, there was a simplistic view that if we got vaccinated or survived a natural infection, we could remain protected from COVID-19 for the rest of our lives. Proponents of herd immunity claimed that they could ‘vaccinate their way out of the pandemic’. Understandably, when vaccines arrived towards the end of 2020, the world was jubilant. There were optimistic projections by vaccine-manufacturers who presented their best results - which was an impressive, albeit short-term reduction in the incidence of symptomatic COVID-19.
However, the early mRNA vaccine trials that declared an efficacy of 95% did not look at asymptomatic infection, transmission or longevity of protection.
Although vaccines initially reduced the risk of infection, the protective effect rapidly waned after a few months – and breakthrough infections were increasingly reported. Boosters arrived, but the problem did not go away. In fact, up to 65% of individuals who had recently received an mRNA booster dose developed breakthrough infections. It was clear that these injectable or systemic vaccines did not provide sufficient immunity at the gate of entry of the virus, which was the upper respiratory mucosa.
Vaccines had a more sustained effect on preventing the progression to severe disease, which fortunately has remained stable since. However, it must be kept in mind that the total number of deaths in any region is directly linked to the total number of infections. As a result, when public health measures were removed in highly vaccinated nations such as Portugal, infection became widespread - and deaths increased.
Unless infection rates are kept in check, death rates cannot be minimised.
2. What is the difference between breakthrough infection and reinfection?
Infections occurring among vaccinated people are called breakthrough infections. They are less likely to cause death when compared to COVID-19 occurring in an unvaccinated individual.
When the virus infects someone who had already been infected earlier, it is called a reinfection. This can occur among vaccinated as well as unvaccinated individuals.
3. Reinfections are trending now.
Two-and-a-half years into the pandemic, repeated infections have become the norm. It is not uncommon for doctors to encounter patients who have had multiple bouts of COVID-19.
In our recent study from India, we reported that at least 15% of people with COVID-19 were having it for the second time or more, and this was despite being vaccinated. Doctors practising in various parts of India are already reporting that up to 40% of COVID-19 patients they are seeing now are in fact suffering from reinfections. This corroborates with experience from around the world.
Thus, reinfection is the trending term in 2022.
The ability of rapidly evolving Omicron sub-lineages to escape immunity from prior vaccination as well as from natural infection has compounded this problem. As a result, reinfection occurring within a few weeks is not uncommon. For instance, the US Health Secretary Mr Xavier Becerra recently had two bouts of COVID-19 within a span of one month, in spite of being fully vaccinated and boosted.
4. Different phases of the pandemic, different problems to tackle.
In 2020, there being no protection from vaccines or prior immunity, surviving COVID-19 was a formidable challenge. Mortality rate was relatively high; millions of people lost their lives (mortality rate is defined as the probability of dying if infected). Deaths were not limited to vulnerable segments of the population; many healthy young adults also succumbed.
Halfway through 2022, the equation is different. The mortality rate has reduced, and this is believed to be chiefly the effect of acquired immune memory.
On the flip side, the rate of infection has increased, which means a larger number of people are getting infection at a time. As the virus adapted to escape immunity, reinfections became common. When that happened, there was a popular narrative that reinfections were a good thing, and ‘helped build more immunity’.
All narratives have their proponents; this one was popular among people who were keen to discard masks and other public health measures. Recent research has however shown that Omicron is not a ‘natural booster’, as some experts had claimed earlier.
The question now is, what are the long-term outcomes among people who get repeated infections.
5. Breakthrough infections are associated with long-term setbacks.
Researchers have been studying the further clinical course of those who survived breakthrough infection.
Recent studies published in Nature have shown that among those who survive breakthrough infection, there is increased risk of death for at least six months, and an extended risk of cardiovascular outcomes for up to a year - when compared to people without breakthrough infection.
6. What are the potential drawbacks of getting infected repeatedly?
Earlier during the pandemic, several experts had hinted that reinfections will be milder or asymptomatic. However, we are now finding that is not always the case.
Recent US research on reinfections reported a cumulative effect, with worse outcomes occurring among those who got infected a greater number of times.
In addition, there is an increased risk of post-acute sequelae or Long COVID following reinfections.
The additional risk of death and Long COVID was lower among those who were vaccinated, compared to unvaccinated individuals.
7. How could this impact future public health policy?
With reduced mortality rates, the absolute number of undesirable outcomes might seem insignificant at first glance. However, when reinfections occur in large segments of the population, the collective impact could be substantial. The limitations of COVID-19 vaccines being well-established now, it is important to resort to evidence-based preventive public health strategies to reduce the spread of this virus in the community. Contrary to public perception, such strategies need not be restrictive as in the case of lock-downs. Improving ventilation and enabling indoor masking in public spaces are examples.
In this context, it is worth pointing out that China, a country that has done extensive research on viruses, is pursuing a zero COVID strategy - even after vaccinating its population. Although criticised by western nations for its intermittent lockdown measures, China clearly appears concerned about letting this virus run unchecked among its vast population.
8. Knowledge is changing, and that’s a good thing
Knowledge about this new virus is rapidly evolving. Past narratives, mostly based on convenience and irrational optimism, are being proven wrong. The virus appears to be here to stay and is adapting to infect more people at progressively shorter intervals. Unfortunately, we do not have a fully effective vaccine that can prevent infection, although research works are going on.
In fact, there are several viruses against which there is no vaccine or antiviral drug available yet. Such is the nature of these organisms.
However, public health measures have been able to reduce the disease burden of all infectious diseases. For instance, cholera was controlled by providing clean water rather than by distributing antibiotics. Likewise, attention to air hygiene holds the key to COVID-19.
Being a cyclical disease, ups and downs are to be expected with COVID-19, as is the case with several other viruses that infect man. During times of a surge, extra caution will be required. This virus spreads through aerosols, which are basically tiny weightless fluid particles that float in the air for hours, carrying infectious virus particles within. When these particles reach other individuals sharing the same space, infection spreads. This is the rationale for avoiding unmasked mass gatherings in closed, ill-ventilated spaces.
In summary, we now live in a different world - one that has been infested by a new virus that we cannot eliminate. Vaccines continue to protect against severe disease, but are not good at preventing infection or transmission. Reinfections are increasingly common, and the intervals between infections are getting shorter. Getting infected repeatedly with SARS-CoV2 appears to be associated with increased long-term risk of death and cardiovascular outcomes, and must be avoided to the extent possible. The virus continues to dominate, and optimistic predictions even by renowned experts are repeatedly being proved wrong. Meaningful public health measures need to be put in place before we have large sections of our population suffering from the ill-effects of repeated infections.
Attention to air hygiene holds the key
Cholera was controlled by providing clean water rather than by distributing antibiotics.
Getting infected repeatedly with SARS-CoV2 is associated with increased long-term risk of death and cardiovascular outcomes, and must be avoided to the extent possible.
Attention to air hygiene holds the key to COVID-19.
Although vaccines protect against severe disease, they are not very effective at preventing infection.
COVID-19 is not the common cold; it can also affect the heart, brain and blood vessels.
Scientific research apart, clear and effective public communication is an important part of pandemic control.
Knowledge about this new virus is rapidly evolving, and past narratives, mostly based on convenience and irrational optimism, are being proven wrong. The virus appears to be here to stay and is adapting to infect more people at progressively shorter intervals.