Why you will need one more shot to stay safe from Covid

A SHOT OF HOPE

Why you will need one more shot to stay safe from Covid

Covid vaccines were made in the middle of a pandemic with the mantra of ‘less is more’, but now that supplies have improved, experts say it’s time to consider giving three doses for optimum protection

Abhilash.Gaur@timesgroup.com

22.10.2021

Half of India has now got at least one Covid shot, but in Israel the government is stocking vaccines for a possible fourth dose. Through the summer it gave third shots to the 60-plus group, and in late-August made everyone over 12 eligible.

At the other end of the vaccination scale, only 7% of people in Africa have got a shot. Israel’s vaccine push, therefore, seems excessive. Without naming any country, the WHO has called booster dosing against Covid ‘immoral’. “To start boosters is really the worst we can do as a global community,” WHO director general Tedros Adhanom Ghebreyesus said.

Nevertheless, more and more rich countries are giving booster shots and, maybe, you too have been wondering when you will get yours. Here’s why booster dosing for Covid has started looking inevitable.

FADING IMMUNITY

Rich countries started giving third doses because infections among the fully vaccinated were rising, supporting the findings of studies that showed immunity created by vaccines declines within months. For example, a British study found the AstraZeneca/Covishield vaccine’s ability to prevent mild Covid after the second dose fell from 67% to 47% after 20 weeks.

From the start of the pandemic scientists have said vaccines that turn Covid into a mild flu-like illness – even if they don’t prevent infection – would be good enough, but the UK research shows vaccines also lose some of their ability to prevent serious illness and hospitalisation with time. Overall, the protection against severe disease and hospitalisation slipped from 95% to 77%, a BBC report says.

The sharpest decline in protection occurred in the 80-plus age group while the younger lot were well protected with even two doses. That’s why, for now, the UK has recommended a third dose for only those over 50.

Likewise, data from Israel shows people over 60 who got their second dose more than five months ago are at three times higher risk of infection than those vaccinated recently. However, two weeks after the third dose their risk of infection reduces by 11.3 times, David O’Connor, professor of pathology and laboratory medicine at the University of Wisconsin, writes in The Guardian.

WHY IMMUNITY WANES

In an article for The Wall Street Journal, Jo Craven McGinty says vaccine effectiveness depends on more than one factor, including the strength of the initial immune response, rate of antibody decay, the pathogen’s tendency to mutate, and also the part of the body it infects. That’s why measles shots are good for life while flu shots are needed every year.

She says Covid is still so new that scientists don’t have an exact measure of its “threshold of protection” or the level of immunity needed to prevent illness. So it’s hard to say with certainty whether two doses are enough, or a third will suffice, or whether we might need booster shots every year.

Also, the Covid virus mutates a lot more than the measles and chicken pox viruses. There have been eight major variants, including Delta, in less than two years. The Beta variant first found in South Africa reduced the efficacy of all vaccines tested against it.

Another problem with Covid, McGinty says, is that the virus replicates in the lower as well as the upper respiratory tracts. Vaccines can prevent severe disease because they don’t allow it to take root in the lungs and lower body, where the blood circulation is good, but the nostrils remain prone to infection as the blood circulation is not so good there.

Also, vaccines that contain a live but weakened form of the disease-causing germ (measles and chickenpox, for example) provide the longest protection, but none of the Covid vaccines is of this type. The mRNA vaccines from Pfizer and Moderna don’t contain a virus at all while those like Covaxin have the dead virus.

3 JABS NEW NORMAL?

While the WHO frowns upon booster dosing, Katherine J. Wu points out in The Atlantic that the third dose might not be a booster, in fact. She says a booster, strictly speaking, is a shot given to shore up flagging immunity. For example, you need a tetanus booster once every 10 years.

While Covid vaccines were originally tested with two doses – because they were developed swiftly in a pandemic – it is possible that three shots might have been the proper “primary” course. The hepatitis B vaccine, for example, requires a course of three shots. Each dose creates and increases the “quantity, quality, and durability of that defence”.

What if stopping at the second dose means denying yourself full protection? Maybe the third dose isn’t so “immoral” after all.

As O’Connor says, “The newer data suggests that a primary immunisation series followed by an additional dose months later should be the new standard protocol.”