Health

Explained | What is causing a surge in COVID-19 cases in India? 

Due diligence: A healthcare worker conducts a swab test on a vendor as coronavirus cases rise countrywide.

Due diligence: A healthcare worker conducts a swab test on a vendor as coronavirus cases rise countrywide. | Photo Credit: PTI

The story so far: Since early June, there has been a steady increase in the number of fresh daily COVID-19 infections, with June 29 marking a new high of 18,467 cases. But on July 6, the daily fresh infections witnessed a further bump with 18,506 fresh infections. After the third wave peaked in end-January 2022, the number of daily cases had dropped and held steady at a very low level till it began increasing in early June. On July 9, the active caseload as of 9:00 am was more than 1,25,000 with the weekly test positivity rate being 3.86%.

Why has there been a rise in daily infections?

The BA.2 Omicron sub-lineage is still the dominant strain in India. However, many States have reported the presence of BA.4 and BA.5 Omicron sub-lineage variants. While the BA.2 Omicron variant itself spreads quickly, the BA.4 and BA.5 are even more transmissible than BA.2. Also, the BA.4 and BA.5 sub-lineages have an even better ability to evade the immune system and cause infection, which is leading to an increase in cases not only in India but in several countries. In its weekly epidemiological update, the World Health Organization (WHO) on July 6 said that for the week of June 27 to July 3, 2022, “over 4.6 million cases were reported, a figure similar to that of the previous week”. But the number of new infections recorded may not reflect the true spread of the virus as “several countries have been progressively changing COVID-19 testing strategies, resulting in lower overall numbers of tests performed and consequently lower numbers of cases detected,” the WHO cautioned.

In addition to BA.4 and BA.5, India and about half-a-dozen other countries have reported BA.2.75, which is a new sub-lineage of Omicron. The spike protein of BA.2.75 carries nine mutations and the mutations are seen on both the N-terminal domain and the receptor binding domain. Whether the nine mutations will further increase the transmissible nature of BA.2.75 compared to BA.5 and BA.2 remains to be seen. One mutation (G446S) can contribute to significant immune escape, which could mean that reinfections and breakthrough infections could drive the spread of BA.2.75, says Dr. Vinod Scaria, a senior scientist at the Institute of Genomics and Integrative Biology (CSIR-IGIB). The rapid increase in BA.2.75 cases in India in recent weeks “suggest that it might have a growth advantage,” he tweeted.

It is not clear what percentage of fresh cases is caused by BA.4, BA.5 and BA.2.75. But the sudden increase in daily cases after the third wave peaked in end-January 2022 clearly suggests that a new sub-lineage of the Omicron is driving this increase.

Why haven’t the high vaccination coverage and natural infection helped to stop re-infection?

Currently available vaccines have a higher protective effect against hospitalisation, preventing severe disease, and even death. They have very low protective effect against an infection, particularly from the Omicron sub-lineages. Thus a person who is fully vaccinated and even received a booster shot is vulnerable to get a breakthrough infection. In general, soon after a booster shot, the protective effect against breakthrough infection is modest. But with the Omicron variants showing increasing ability to evade the neutralising antibodies, a recently administered booster shot has an even lower protective effect against breakthrough infection.

Natural infection too has been found to be less protective against re-infection by the Omicron sub-lineages. This is again due to the higher immune escape capability of the Omicron sub-lineages. It has been found that infection with BA.2 does not protect from infection caused by the BA.4 or BA.5 variant. For the same reason, it is likely that infection with BA.5 may not protect against BA.2.75. However, hard evidence to support this is not yet available.

Health experts say the reason why BA.2 infection does not offer protection against BA.4 or BA.5 is because of the higher ability of BA.4 and BA.5 to evade the neutralising antibodies caused by a previous infection. So a person infected with BA.2 can still get reinfected with BA.4 or BA.5

Hybrid immunity caused by vaccination and infection was generally seen to offer slightly better protection against infection. But with the Omicron sub-lineages, even hybrid immunity offers no advantage in terms of protecting against re-infections.

How effective are full vaccination, a booster shot and natural infection against severe disease?

The Omicron variants have so far not turned out to be lethal or causing severe disease and deaths. Since virus transmission takes place before disease onset, the selection pressure faced by the virus is for enhanced transmissibility and not for disease severity. A new variant of concern may be less or more lethal than the current ones but always more transmissible than the currently seen variants. That said, a new variant that is not only extremely transmissible but also more lethal can also arise.

Natural infection, full vaccination with two doses of any COVID vaccine and hybrid immunity greatly reduces the risk of severe disease and death, but its protective effect beyond one year has not yet been studied. But ground evidence suggests that full vaccination protects against severe disease and deaths. A booster shot particularly for the vulnerable population offers greater protection against severe disease. It is therefore advisable that all vulnerable people receive a booster shot as early as possible.

What is the best way to prevent fresh infection?

While all Omicron sub-lineages have extremely high transmissibility, regular and consistent use of good quality face masks together with avoiding crowded places, particularly closed spaces with poor ventilation, can greatly reduce the chances of getting infected.


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Printable version | Jul 16, 2022 4:32:30 pm | https://www.thehindu.com/sci-tech/health/the-hindu-r-prasad-explains-what-is-causing-a-surge-in-coronavirus-cases-in-india/article65619591.ece