Covid-19: New studies show waning vaccine efficiency as CDC recommends call for booster shots

The protection against SARS-CoV-2 offered by Pfizer and Moderna’s vaccines wanes over time, according to three new studies by the US Centers for Disease Control and Prevention (CDC), sparking debate among health experts over the need to administer booster shots. Despite that, the vaccines are largely effective against hospitalisations, the studies found.

Significance of the studies
The studies come on the heels of the US Food and Drug Administration (FDA) authorising booster shots for transplant recipients and people with compromised immune systems in an attempt to protect them against Covid-19 variants.

The US FDA said those who had received shots of either the Pfizer-BioNTech or Moderna vaccines were eligible for a third dose. While there is no update on people who received Johnson and Johnson’s single-dose vaccine, it is likely they will also require booster shots.

The likes of Germany, Israel, and France have already planned out booster shot administration.

The World Health Organisation, meanwhile, placed a moratorium on booster shots earlier this month, citing disparity in vaccinations in low- and high-income countries. WHO Director-General Tedros Adhanom Ghebreyesus had previously emphasised that countries that had already used a significant portion of the global vaccine supply could not use more of it.

Result of the studies
One study, conducted between May 3 and July 25, found that overall effectiveness of the vaccines in all adult age-groups in New York fell to 79.8 per cent from 91.7 per cent despite a relatively stable (between 91.9 per cent and 95.3 per cent) overall age-adjusted effectiveness against hospitalisations.

The study was conducted during high circulation of the virus’ Delta variant, which could be a reason behind the reduced effectiveness of vaccines.

According to another study that was conducted in March-July found that among 1,129 individuals who had received both doses of one of the mRNA vaccines, there was no decline in effectiveness against hospitalisations after six months. It found the effectiveness to be 86 per cent two to 12 weeks after inoculation and 84 per cent after 13–24 weeks. There was sustained effectiveness among groups at risk of severe Covid-19 infecction.

Another March-May study among nursing home residents found that two doses of the mRNA vaccines were 74.7 per cent effective. This study found that the effectiveness declined to 53.1 per cent during June-July when the Delta variant was predominant. The study said a third dose might be considered for long-term care facility and nursing home residents to optimise the protective immune response.

Booster shot eligibility
A third dose has been recommended for moderately or severely immunocompromised people — believed to be more at risk of serious, prolonged illness.

This is because people with weakened immune systems might not build the same immunity after two doses when compared to those who are not immunocompromised. For now, immunocompromised people are eligible for a third dose at least 28 days after the second one.